GPS has a number of inherent weaknesses in terms of availability and integrity of information to provide a position solution that can be relied upon. The use of inertial sensors to provide an augmentation to GPS is a common approach in overcoming these weaknesses.

An Inertial Navigation System (INS) provides position, velocity, orientation and angular velocity by measuring the linear and angular accelerations applied to the system. Spirent offers a number of systems designed to simulate the inertial sensor outputs coherently with simulated GPS RF, thus enabling the inertial receiver elements to be tested. In addition, Spirent has a turntable option available for stimulation of embedded inertial sensors, again coherent with simultaneous GPS simulation.

The use of GPS with inertial technology was first developed in the military environment, where accurate inertial sensors were coupled with GNSS receivers to give a blended navigation solution. Recently, GPS coupled with inertial sensors has been used in civilian, commercial and consumer applications e.g. in car navigation system where GPS may have problems tracking in a tunnel or in built up environments, the inertial sensors would allow you to keep navigating until the location became more favourable to GPS receptivity. However, the main disadvantage of using just inertial sensors is known as ‘open loop back systems’ whereby any errors become cumulative over time.

Testing inertial sensors themselves is quite problematic as they have to moved, often violently, to simulate real field conditions – Spirent has developed a number of systems to enable laboratory based simulation of systems integrating GPS and inertial sensors including – SimINERTIAL for military and high precision, SimAUTO for automotive and portable consumer devices.